From L2 to S3. Additional neurons needed for innervation of lower limbs

What is the conus medullaris?

Very end of spinal cord. The tapered end of the spinal cord which includes sacral spinal cord segments

How many spinal cord segments are there?

31. 8 cervical. 12 thoracic. 5 lumbar. 5 sacral. 1 coccygeal.

31 pairs of spinal nerves; each segment gives rise to a pair of spinal nerves

What kind of nerves are in the lateral horn? in the intermediate gray?

Lateral horn has autonomic motor while intermediate gray has interneurons

What are the three layers of the meninges?

Dura mater, Arachnoid, Pia mater

Describe the dura mater

The outermost later.
-composed of dense connective tissue
-2 layers: periosteal layer (attaches to vertebrae) and meningeal layer (envelopes spinal cord)
-Between the periosteal and meningeal layers in an epidural space (fat filled and has a venous plexus)
-Between the meningeal layer and Arachnoid is a subdural space which is just a potential space

Describe the Arachnoid

-Located deep to the dura
-Is avascular (no vessels)
-tissue is thin and transparent
-deep to arachnoid is the subarachnoid space (filled with CSF)

What is a lumbar cistern?

-inferior part of the subarachnoid space
-located in lumbar region
-region where samples of CSF can be taken from
-ends inferiorly to at S2 vertebral level

-threadlike strand of the pia mater that leaves the conus medullaris and descends among the nerve roots of the cauda equina.
-Courses inferiorly through the middle of the lumbar cistern and is surrounded by the cauda equina (bundle of spinal roots)
-Becomes covered by the arachnoid and dura inferior to the S2 vertebral level to form the coccygeal ligament

What is the coccygeal ligament?

This ligament anchors the spinal cord and meninges inferiorly to the coccyx

What is the spinal nerve made of?

Union of dorsal and ventral roots.
-contains both sensory and motor axons.
-leaves vertebral column via intervertebral foramen
-distal to the intervertebral foramen, it divides into two braches (rami)

What is the dorsal primary ramus?

-different from dorsal root
-has both sensory and motor fibers
-innervates skin and deep muscles of the back

What is the ventral primary ramus?

-bigger than dorsal ramus
-innervates upper and lower limbs, and anterolateral trunk
-innervates superficial and intermediate muscles of the back
-contains both sensory and motor fibers
-contributes to major plexuses in the body (brachial plexus)

-bundle of spinal nerve roots in the subarachnoid space caudal of the termination of the spinal cord
-dorsal and ventral roots of lower lumbar and sacral spinal nerves
-sacral end of spinal cord (conus medullaris) is opposite the disc between L1 and L2
-lower spinal nerve roots must travel within the lumbar cistern to reach their respective intervertebral foramina
-within the lumbar cistern, they surround the filium terminale